Valve regulated lead acid battery

ABSTRACT

A valve-regulated lead acid (VRLA) battery cell ( 2,40 ) has positive and negative plates ( 10,11,41,42 ) separated by separator media ( 12,43 ) and held together under pressure. The separator is adapted to support therein an electrolyte. Each plate has a first single or plurality of tabs ( 12,13,46 ) on a first side and a second single or plurality of tabs ( 15,16,47 ) on a second side of the plate, each tab being connected to a busbar ( 17,18,49,50 ) to form positive and negative busbars on each of the first and second sides of the plate. The cell may be alternatively configured in a spirally-wound arrangement or in a prismatic arrangement of flat plates. The cell may be constructed of a plurality of such positive and negative plates. A VLRA battery ( 1, 40 ) may be constructed of one or a plurality of such VLRA cells, in which case the busbars of neighboring cells are connected by welded joints. The busbars are serviced by at least plural pairs of positive and negative terminals ( 24,25,33,34,52,53,54,55 ).

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/967,663, filed Oct. 18, 2004 now abandoned, which is a continuationof U.S. patent application Ser. No. 10/336,615, filed Jan. 4, 2003, U.S.Pat. No. 6,815,118 (B1), which is a divisional of U.S. patentapplication Ser. No. 09/707,753, filed Nov. 6, 2000, U.S. Pat. No.6,555,265 (B1), which claims the benefit of U.S. Provisional ApplicationNo. 60/195,079 filed Apr. 6, 2000.

BACKGROUND OF THE INVENTION

The present invention relate to valve-regulated lead-acid (VRLA)batteries that are suitable for use in hybrid electric vehicles (HEVs)and electric vehicles (EVs).

Exhaust emissions from transport vehicles are a major cause of bothgreenhouse gas build-up and urban pollution. Concern over these issueshas resulted in the introduction of new anti-pollution legislation thatsignificantly restricts exhaust emissions from internal combustionengines. Some countries have been more severe in their approach and havelegislated that a certain number of vehicles sold must have either lowor zero emissions. Such vehicles include electric vehicles (EVs) andhybrid electric vehicles (HEVs). The success of this initiative hingeson the development of vehicles that have both appropriate performanceand lifetime cost characteristics.

HEV battery packs are subjected to multiple charge-discharge cyclesbelow a full state-of-charge (SoC). Such duty can cause a localized,irreversible build-up of lead sulphate. This impairs batteryperformance. Similar buildups, along with associated high temperaturesand uneven temperature gradients can also occur within EV batteries thatare subjected to rapid recharge and discharge conditions.

The specification of U.S. Pat. No. 4,760,001 discloses a batterycomprising negative plates made from expanded lead-coated copper havingtabs formed by a copper strip extending across the plate. In one form ofthe battery, the copper strip extends beyond exposed edges of thenegative plate to form lugs or tabs on opposite sides of the plate. Thisleads to sub-optimal location of the tabs with respect to drainage ofcurrent and heat. Furthermore, lead-coated expanded copper plate areconsiderably more expensive to make than expanded lead plates. Inaddition, such batteries would not be suited to HEV or EV use because oftheir high cost and additional weight.

The specification of U.S. Pat. No. 4,983,475 discloses a battery designin which each plate has dual tabs on opposed sides and each tab isconnected to a corresponding negative or positive busbar. Each of thebusbars are in turn connected by diagonally disposed straps. The purposeof the dual tabs and straps is to improve the electrical characteristicsof the battery. However, the batteries described in the specificationwould not be suitable for HEV and EV use because they are only 2 voltbatteries and the straps add unnecessary weight. Furthermore, the strapsabsorb valuable space.

The specification of U.S. Pat. No. 4,603,093 discloses battery cellshaving two or more tabs per plate. The purpose of the multiple tabs isto improve energy density and power density. This design permits the useof longer shallower plates than previously contemplated. However, themultiple tabs are located on one side of the plate.

The specification of WO 99/40,638 describes cells having plates of theopposite geometry as that described in the specification of U.S. Pat.No. 4,603,093. In other words, the plates are narrow and deep. In orderto improve the availability of current from cells containing plates ofthis design, tabs are placed on opposite sides of the plate and currentfrom one end is transferred to the other by means of a lead-platedcopper strap. This improves current availability because copper is abetter conductor than lead. Although this design includes tabs onopposed sides of the plate, it does not contemplate terminals on opposedsides of the battery. Consequently, current still has to be transferredfrom one side of the plate to the other in order to connect with therelevant terminal. Furthermore, the strap adds to the weight of thebattery.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a valve regulated leadacid (VRLA) cell comprising a positive and negative plate separated by aseparator and held together under pressure. Preferably, the pressureapplied to the cell lies in the range from 20 to 100 kPa. The separatorsupports therein an electrolyte. Each plate has a first single orplurality of tabs on a first side of the plate, and a second single orplurality of tabs on a second side of the plate. Each tab is connectedto a busbar to form positive and negative busbars on each of the firstand second sides of the plate.

The cell may be a spirally-wound cell, or a prismatic cell. Thespirally-wound cells may be either 2V cells, or manufactured to producemonoblocs with a total voltage of 4 and higher. Spirally-wound cellshave current takeoffs at both the top and bottom of the both negativeand positive plated (hitherto referred to as spirally-wound batterieswith bidirections current takeoffs). The prismatic cell preferablyincludes a plurality of such positive and negative plates separated byseparators. A plurality of cells may be connected in series.

In another aspect, the invention provides a VRLA battery comprising aplurality of cells joined in series, wherein each cell includes one ormore positive and negative plates separated by one or more separatorsand held together under pressure. Preferably, the pressure applied tothe cell lies in the range from 20 to 100 kPa. The separator supportstherein an electrolyte. Each plate has a first single or plurality oftabs on a first side of the plate, and a second single or plurality oftabs on a second side of the plate. Each tab is connected to a busbar toform positive and negative busbars on each of the first and second sidesof the plate. Each cell may be connected to a neighboring cell by weldedjoints between alternate positive and negative busbars. These welds arepreferably, but not exclusively, through the cell-case wall or over thetop of the cell wall. Each cell may be independently sealed airtight.Alternatively, all the cells in the battery may have a commonhead-space. A plurality of batteries may be connected in series.

The separator used in the invention can be made of absorptive-glassmicro-fiber, or can be compatible with the use of gelled-electrolyte.Alternatively, any separator material that can withstand reasonablelevels of compression (for example, pressure greater than 20 kPa) issuitable.

In another aspect, the invention provides an electric or electric hybridvehicle (eg., EV or HEV) that includes one or more such cells orbatteries.

The invention provides several advantages. VRLA cells and batteries ofthe invention are light-weight and low cost. Such cells and batterieshave the capacity to deliver substantial current flows while in apartial-state-of-charge (PSoC) condition over a large number of cycles.Also, under high charge and discharge conditions, cells and batteriesaccording to the present invention maintain a much lower and almostisothermal internal battery temperature, compared to that experienced inprior art designs. The dual-tab design does not develop significanttemperature gradients during either HEV or PSoC/fast-charge EV duty anddoes not suffer from preferential sulphation. All these features providedistinct advantages for vehicles applications.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings certain exemplary embodiments of theinvention as presently preferred. It should be understood that theinvention is not limited to the embodiments disclosed as examples, andis capable of variation within the scope of the appended claims. In thedrawings,

FIG. 1 is a top plan view of a valve-regulated lead acid battery inaccordance with the invention having a dual-tab, flat-plate arrangement,wherein a lid of the battery case is removed from the view to bettershow the interior arrangement;

FIG. 2 is a bottom plan view of the dual-tab flat-plate battery of FIG.1 except with a base of the battery case being removed from the view;

FIG. 3 is a side elevation view the dual-tab, flat-plate battery ofFIGS. 1 and 2 except with the near sidewall of the battery case beingremoved from the view partly to show better the inter-cell welding,which is arranged vis-a-vis over the cell wall partitions;

FIG. 4 is a side elevation view comparable to FIG. 3 except showing analternate arrangement of inter-cell welding, which in this view isarranged not over but through the cell wall partitions;

FIG. 5 a is a top plan view of an alternate embodiment of avalve-regulated lead acid battery in accordance with the inventionhaving a spirally-wound cell arrangement with bidirectional currenttakeoffs, showing both positive and negative busbars;

FIG. 5 b is a side elevation view of a spirally-wound cell withbidirectional current takeoffs of FIG. 5 a, showing busbars at both thetop and bottom of the unit;

FIG. 6 is a graph showing both end of discharge voltage (EoDV) andtemperature (T) profiles, as graphed against number of test cycles, toafford comparison between a representative single-tab battery of theprior art and a flat-plate dual-tab battery in accordance with theinvention, under conditions representative of an HEV cycle rate of 2 C;

FIG. 7 is a comparable graph showing end of discharge voltage (EoDV) andtemperature (T) profiles, as graphed against number of test cycles, toafford comparison between the given single-tab battery of the prior artand the flat-plate dual-tab battery in accordance with the invention,except under conditions representative of an HEV cycle rate of 4 C;

FIG. 8 is a graph showing only end of discharge voltage (EoDV) profiles,as graphed against number of test cycles, to afford comparison betweenthe given single-tab battery of the prior art and the flat-platedual-tab battery in accordance with the invention, under conditionsrepresentative of PSoC/fast-charge EV duty; and

FIG. 9 is a graph showing only temperature (T) profiles, as graphedagainst number of test cycles, to afford comparison between the givensingle-tab battery of the prior art and the flat-plate dual-tab batteryin accordance with the invention, likewise under conditionsrepresentative of PSoC/fast-charge EV duty.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top plan view of a valve-regulated lead acid (VRLA) battery1 in accordance with the invention, which in general comprises aflat-plate arrangement. The battery 1 has six cells 2 to 7. Each cell isseparated from a neighboring cell by means of cell partitions 8. Thecells are encased in a battery casing 9. Each cell comprises negativeplates 10 separated from positive plates 11 by means of separators 12.As shown in FIG. 3, each negative plate has tabs 13 and 14 protrudingfrom opposite sides. Similarly, each positive plate has tabs 15 and 16protruding from opposite sides.

Referring back to FIG. 1, each of the tabs 16 attached to the positiveplates are connected to positive busbars 17 and each of the tabs 14attached to the negative plates are connected to negative busbars 18.

The negative busbar 18 of cell 2 is connected to positive busbar 17 ofcell 3 by means of inter-cell welded joint 19. Likewise the negativebusbar 18 of cell 3 is connected to the positive busbar 17 of cell 4 bywelded joint 20. And so on, such that, similarly, cells 4, 5, 6 and 7are connected to each other by weld joints 21, 22 and 23, therebyconnecting each of the cells in series to form a battery having anominal capacity of 12 volts. FIG. 3 shows better the inter-cell weldingsuch as arranged vis-a-vis over the cell wall partitions. FIG. 4 is acomparable view to FIG. 3 except showing an alternate arrangement ofinter-cell welding (ie., 20′), which in this view is arranged not overbut through the cell wall partitions. In FIG. 1, a terminal 24 isconnected to the positive busbar 17 of cell 2 and a terminal 25 isconnected to the negative busbar 18 of cell 7.

When viewed from the bottom as in FIG. 2, the battery has a similarstructure with positive busbars 26 connected to positive tabs 15 thatare attached to the positive plates and negative busbars 27 connected totabs 13 that are attached to the negative plates. Similarly, cells 2, 3,4, 5, 6 and 7 are connected by welded joints 28, 29, 30, 31 and 32 onalternate sides of the battery. FIG. 2 also shows that busbar 26 of cell2 has positive terminal 34 connected to it and negative busbar 27 ofcell 7 has negative terminal 33 connected to it. Therefore, referring toboth FIGS. 1 and 2, the battery 1 has two positive terminals and twonegative terminals, as shown by either FIGS. 3 or 4 in a single view,which latter views also show that the cells are provided withrelief-valves “V.”

In operation, current is drawn from the top and the bottom of each platethrough busbars on the top and the bottom of the cell through thebusbars into respective positive and negative terminals, therebyproviding a much shorter path on average from the plate to a terminal.This minimizes the generation of heat as a result of resistive effects.Similarly, this design provides shorter path for dissipation of heatfrom the plates through the busbars and out through the terminals.

FIG. 5 a is a top plan view of another embodiment of a VRLA battery 40in accordance with the invention, comprising an arrangement ofspirally-wound plates. The battery 40 comprises a negative plate 41, apositive plate 42 and a separator 43. As seen in FIG. 5 b, the positiveplate 42 has four positive plate tabs 44 at the top and four positiveplate tabs at the bottom. Similarly, negative plate 41 has four negativeplate tabs 46 at the top and four negative plate tabs 47 at the bottom.

The positive plate tabs 44 are connected to positive busbar 48 at thetop of the battery and positive plate tabs 45 are connected to positivebusbar 49 at the bottom of the battery. Similarly, negative plate tabs46 are connected to negative busbar 50 at the top of the battery and thenegative plate tabs 47 are connected to negative busbar 51 at the bottomof the battery.

Positive busbar 48 is connected to positive terminal 52, negative busbar50 is connected to negative terminal 53, positive busbar 49 is connectedto positive terminal 54 and negative busbar is connected to negativeterminal 55.

It will be appreciated that tabs 44 and 45 at the top and bottomrespectively of positive plate 42 are spaced at distances that decreaseas the interior of the spirally bound battery is approached so that tabs44 and 45 coincide with busbars 48 and 49 respectively. Clearly,therefor, the exterior of the spirally wound plate will not drain aswell as the interior. This problem could be overcome by providingadditional busbars and corresponding tabs at the outer ends of thespirally wound plates.

FIGS. 6 through 9 provide graphical evaluation of how the flat-platedual-tab battery 1 in accordance with the invention compares to arepresentative single-tab battery of the prior art under variousconditions representative of HEV duty in some instances and EV duty inanother.

By way of background, HEV battery packs are required to operate for manycycles below a full SoC. They are also subjected to high charge anddischarge currents. The operation of commercially available, VRLAbatteries under such duty has been shown to result in localizedirreversible formation of lead sulphate in battery plates.

As stated, a flat-plate version of the dual-tab battery 1 in accordancewith the invention has been evaluated along-side a representativesingle-tab battery of the prior art of equivalent size, weight andcapacity and under a simulated HEV profile that is known to encouragethe formation of localized, “refractory” lead sulphate. The test cyclewould involve the following steps:

-   -   (i) discharge (2 C rate) to 50% SoC;    -   (ii) charge at specified rate (ie., 2 C˜21½ A; 4 C˜43 A) for 1        minute;    -   (iii) rest at open circuit for 10 seconds,    -   (iv) discharge at specified rate (2 C˜21½ A; 4 C˜43 A) for 1        minute;    -   (v) rest at open circuit for 10 seconds;    -   (vi) repeat (ii)-(v) until voltage decreases to 10 V at the end        of step (iv) or increases to 15 V at the end of step (ii).

(Note:—all charges and discharges are based on Ahs).

To turn to FIG. 6, it is a graph showing both end of discharge voltage(EoDV) and temperature (T) profiles, as graphed against number of testcycles, to afford comparison between the representative single-tabbattery of the prior art and the flat-plate dual-tab battery 1 inaccordance with the invention, under conditions representative of an HEVcycle rate of 2 C (ie., charge and discharge occurring at a specifiedrate, which here corresponds to about 21½ A).

When subjected to the foregoing 2 C HEV duty, what happened was theprior art battery and the inventive battery 1 delivered 6900 and 8800HEV cycles, respectively, before their end-of-discharge-voltages(EoDV's) dropped to 10 V (FIG. 6) and equalization charging wasrequired. The higher number of cycles gotten by battery 1 in accordancewith the invention represents a 25% decrease in the frequency ofequalization. Such improvements are required by HEV manufacturers, sothat negative plates are no longer a weak point in HEV batteries,thereby allowing equalization charging of the batteries to be performedduring routine vehicle servicing or eliminated entirely.

Now to turn to the matter of temperatures, the temperature of the priorart battery, measured externally at the side of the battery case,increased gradually during operation and reached 65° C. at thecompletion of 6900 HEV cycles (FIG. 6). Previous studies have shown thatthe internal temperatures of batteries can be up to 20° C. higher thanexternal temperatures under such duty. Hence, it is considered likelythat continued operation of the prior art battery could have resulted inthermal runaway, a condition that can have severe safety implications.

The temperature of the battery 1 in accordance with the inventionremained at 38±2° C. through out its cycling period (FIG. 6). This isalmost 30° C. cooler than that of the prior art battery. Obviously, thebattery 1 in accordance with the invention is much less susceptible totemperature increases (and therefor, thermal runaway) under extended HEVoperation than the prior art battery. This performance characteristic isvery attractive to HEV manufacturers as the cooling requirements aremuch simplified. Also, the lower operating temperature should reduceboth corrosion of the positive grid and degradation of the expander usedin the negative plate. Moreover, it will minimize the internalresistance of the battery 1 in accordance with the invention.

In summary, the operating temperature of the battery 1 in accordancewith the invention under HEV duty is much reduced relative to that ofrepresentative prior art batteries having just single current takeoffs.The inventive battery 1 provides a considerably longer cycling periodbetween equalization charges than the prior art battery, a factor thatis also very attractive to HEV manufactures.

FIG. 7 is a graph comparable to FIG. 6 in that it likewise shows end ofdischarge voltage (EoDV) and temperature (T) profiles, as graphedagainst number of test cycles, for comparison of the given single-tabbattery of the prior art to the flat-plate dual-tab battery inaccordance with the invention, except under conditions representative ofan HEV cycle rate of 4 C.

More particularly, the performance of the test battery 1 in accordancewith the invention and the prior art battery were evaluated under an HEVduty (see above) with a charge and discharge rate of 4 C. The increasein charge and discharge rate from 2 C to 4 C was expected to cause aconsiderable increase in the operating temperature of the batteries.Hence, as a precaution, a temperature probe was inserted in bothbatteries in the middle of the third cell (from the positive terminal)between the most central negative plate and adjacent separator. Thetemperature was also monitored externally at the hottest area on thecase.

After 50 cycles, the external and internal temperatures of the prior artbattery reached 50 and 70° C. respectively (FIG. 7). At this state, itwas considered that continued operation of the battery would likelyresult in thermal runaway, and in the interests of safety, it wasremoved from service. By contrast, the battery 1 in accordance with theinvention operated for 120 cycles before the same external temperaturelimit was reached. Hence, as with 2 C HEV operation (see above), thepresence of the second current takeoff significantly reduces theoperating temperature of the battery 1 in accordance with the invention,relative to that of the representative prior art battery having only onetab per plate.

FIG. 8 is a graph showing only end of discharge voltage (EoDV) profiles,as graphed against number of test cycles, to afford comparison betweenthe given single-tab battery of the prior art and the flat-platedual-tab battery in accordance with the invention, except here underconditions representative of partial state-of-charge (PSoC)/fast-chargeEV duty.

By way of background, fast charging has been demonstrated as a methodfor overcoming the limited range of lead-acid powered EVs. Also,previous studies have shown that PSoC operation (eg., continued cyclingbelow a full SoC) can offer remarkable improvements incycle-life/lifetime energy, available from selected VRLA batteries. Itis also now known that the combination of fast-charge and PSoC duty canimprove both the effective range of EVs, and the cycle-life/lifetimeenergy of the battery pack. As this type of EV operation is similar toHEV duty, ie., fast charge (up to 12 C) and extended operation within afixed SoC window, it was decided to evaluate a test battery inaccordance with the invention under PSoC/ft-charge EV conditions.Accordingly, the battery 1 in accordance with the invention and therepresentative battery of the prior art were operated continuously underthe following three regimes applied sequentially.

Regime 1.

-   -   The battery is discharged from 100% SoC at a given C rate of 21½        A to a nominal 20% SoC (based on Ahs).

Regime 2.

-   -   The battery is charge at 6 C (129 A) from a nominal 20% SoC        until it reaches a nominal 80% SoC (based on Ahs). The battery        is then discharged at the C rate (21½ A) to a nominal 20% SoC        (based on Ahs). The charge-discharge operation between 20 and        80% SoC without full recharging is referred to as a “PSoC        cycle.” The PSoC process is continued for 24 PSOC cycles, or        until the battery voltage at the end of discharge decreases to        11.1 V, at that point the battery is deemed to be at 10% SoC,        eg., an initial PSoC operating window of 20-80% has become        10-70% SoC.        -   (Note:—one set of 24 PSoC cycles is referred to as a “master            cycle”).

Regime 3.

-   -   (i) The battery is charged at 6 C until the current falls to 5        A;    -   (ii) The battery is then equalized with a constant current for a        specified time.

The results of the cycling, expressed in terms of the end-of-dischargevoltage (EoDV) at the completion of discharge in Regime 2, are shown inFIG. 8. The EoDV of the prior art battery initially increases inresponse to a rise in battery temperature, caused by the commencement offast charging. The EoDV then decreases steadily from 11.75 to 11.45 Vduring the remainder of the master cycle, presumably as a result ofcharging inefficiencies. The EoDV recovered after equalization charging(Regime 3), but then decreased gradually to 11.45 V during the secondmaster cycle. The EoDV after the 1st discharge of the third master cyclehad decreased to 11.15 V, compared to 11.45 V during the first andsecond master cycles. This “irreversible” degradation of the EoDVcontinued, with the battery voltage reaching the cut-off limit of 11.10V during the last discharge of the fourth master cycle. In allsubsequent master cycles, the battery was unable to deliver 24 cyclesbefore reaching the cut-off voltage.

The EoDV of the battery 1 in accordance with the invention remained at amuch higher level throughout PSoC/fast-charge operation, compared tothat of the representative battery of the prior art (FIG. 8). Forexample, the EoDV of the inventive battery 1 during the last dischargeof the first and final master cycles were 11.70 and 11.50 V,respectively, compared 11.45 and 11.10 V for the prior art battery.Hence, the battery 1 in accordance with the invention is more resistantto capacity loss under PSoC/fast-charge duty and, as a consequence, wasable to deliver the required number of PSoC cycles throughout all thetesting period.

Both the prior art battery and the battery 1 in accordance with theinvention used in these experiments was fitted with three internalthermocouples in order to measure “actual” operating temperature of thebatteries during PSoC/fast-charge duty. The probes were installed in thethird cell and were positioned between the middle negative plate andadjacent separator in the following positions:

-   -   (i) 1 cm from the top of the cell group;    -   (ii) middle of the cell group;    -   (iii) 1 cm from the bottom of the cell group.

FIG. 9 shows the internal temperature of both batteries at thecompletion of charging during a typical master cycle. A temperaturegradient formed quickly in the prior art battery during initialoperation. After four cycles, the internal battery temperature reached90, 75 and 70° C. at the top, middle and bottom, respectively. Theextent of the rise was surprising, given that the external temperature,measured at the hottest point on the outside of the battery case, waslimited to 55° C.

The internal temperature of the dual-tab battery 1 in accordance withthe invention increased gradually during initial PSoC/fast-chargeoperation, reaching approximately 65° after 15 cycles. During this time,the temperature differential from the top to the bottom of the batterydid not exceed 5° C. Hence, the battery 1 in accordance with theinvention has both a lower average battery temperature and a reducedinternal temperature differential, compared to the single-tab battery ofthe prior art, when operated under PSoC/fast-charge conditions.

This improvement in performance is due to the dual-tab nature of thebattery 1 in accordance with the invention. In prior art single-tabdesigns, there is a significant increase in current density, ie., thereis “current concentration,” towards the current takeoff, or tab, on thetop of the battery plates during high-rate charge or discharge. Asheating within batteries is related to both the square of the currentand the resistance of the battery (ie., I²R), high, localized currentdensities at the top of the plates can lead to large heating effects inthese regions. The inclusion of a second current takeoff in accordancewith the invention at the bottom of the plate leads to a lower, moreeven current density with the plate, thus reducing the overall amount ofheat produced. Moreover, the dual-tab battery 1 in accordance with theinvention provides even heat dissipation which results in eventemperatures throughout the battery.

It has been demonstrated that the operation of the VRLA batteries underHEV duty can cause the build up of “refractory” or “hard” lead sulphateat the bottom of the negative plates. The phenomenon has been explainedin terms of poor charge acceptance of the negative plates. The discoveryof large internal temperature gradients as a result of highcharge/discharge currents in this study, however, allows therepresentation of an additional hypothesis.

It is well known that if two batteries in parallel are operated atsignificantly different temperatures, the hotter battery will experiencethe highest active-material utilization during discharge. The hotbattery will also accept the greatest amount of charge for a givencharge time and top-of-charge voltage. Given that the top and bottomregions of a battery plate are effectively in parallel, it follows thenthat if they were at different temperatures, they would experiencedifferent degrees of active-material utilization during discharge. Also,the hotter locations would experience a higher degree of overchargerelative to the cooler areas.

This situation will lead to undercharging and sulphation of the coolerregions. The dual-tab design in accordance with the invention does notdevelop significant temperature gradients during either HEV orPSoC/fast-charge EV duty. Presumably it is for that reason that theinventive dual-tab battery does not suffer from preferential sulphation.

The improvements over the prior as shown by the foregoing graphs andwhich have been found for a flat-plate version of the dual-tab battery 1in accordance with the invention are expected to be gotten in comparablemeasure for the spirally-wound version 40 of the dual-tab battery inaccordance with the invention.

The invention having been disclosed in connection with the foregoingvariations and examples, additional variations will now be apparent topersons skilled in the art. The invention is not intended to be limitedto the variations specifically mentioned, and accordingly referenceshould be made to the appended claims rather than the foregoingdiscussion of preferred examples, to assess the scope of the inventionin which exclusive rights are claimed.

1. A battery cell comprising: a positive and negative platecooperatively wound in a spiral assembly and a separator providingseparation therebetween, each plate having a first side thereof and asecond side thereof; first positive and negative busbars connected upwith the first sides of the positive and negative plates, respectively,and second positive and negative busbars connected up with the secondsides of the positive and negative plates, respectively; a sealed casetherefor which extends between spaced first and second ends; and, firstpositive and negative terminals being arranged to protrude from thefirst end of the case and connected to the first positive and negativebusbars, respectively, and second positive and negative terminals beingarranged to protrude from the second end of the case and connected tothe second positive and negative busbars, respectively, whereby saidterminals are distributed to better service the thermal extraction ofthe current-resistive heating effects induced by the plates and/orbusbars and eliminate relative hot-spots from developing in anyunder-served regions.
 2. The cell of claim 1 further comprising eachplate having a first plurality of loci on the first side of the plate,and a second plurality of loci on the second side of the plate, whereineach first and second positive and negative terminal is connected upwith the corresponding plurality of loci of the first or second sides ofthe positive or negative plates, respectively.
 3. A battery comprisingat least two cells according to claim
 1. 4. A battery cell comprising: apositive and negative plate cooperatively wound in a spiral assembly anda separator providing separation therebetween, each plate having a firstside thereof and a second side thereof; a first positive conductorconnected up with the first side of the positive plate and adapted forserving a positive terminal; a first negative conductor connected upwith the first side of the negative plate and adapted for serving anegative terminal; a second positive conductor connected up with thesecond side of the positive plate and adapted for serving a positiveterminal; a second negative conductor connected up with the second sideof the negative plate and adapted for serving a negative terminal; asealed case therefor which extends between spaced first and second ends;and, first positive and negative terminals being arranged to protrudefrom the first end of the case and connected to the first positive andnegative conductors, respectively, and second positive and negativeterminals being arranged to protrude from the second end of the case andconnected to the second positive and negative conductors, respectively,whereby said terminals are distributed to better service the thermalextraction of the current-resistive heating effects induced by theplates and/or conductors and eliminate relative hot-spots fromdeveloping in any under-served regions.
 5. The cell of claim 4 furthercomprising each plate having a first plurality of loci on the first sideof the plate, and a second plurality of loci on the second side of theplate, wherein each first and second positive and negative terminal isconnected up with the corresponding plurality of loci of the first orsecond sides of the positive or negative plates, respectively.
 6. Abattery comprising at least two cells according to claim
 4. 7. The cellof claim 4 wherein: the first positive conductor is connected up withthe first side of the positive plate at a plurality of spaced locations;the first negative conductor connected up with the first side of thenegative plate at a plurality of spaced locations; the second positiveconductor connected up with the second side of the positive plate at aplurality of spaced locations; and the second negative conductorconnected up with the second side of the negative plate at a pluralityof spaced locations.